The objectives of this investigation are to elucidate the genetic interactions in the nocardiae by studying the mechanism(s) of recombination and by exploring the transducing potentials of certain nocardiophage. A survey will also be conducted for additional members of the Nocardia erythropolis mating system. Kinetics of recombination will be studies in crosses conducted in a chemical defined brothe. The high frequency of recombinant recovery obtained from this mating medium (1-2%) provides the opportunity for isolation and characterization of nocardial zygotes. Sucrose gradient centrigugation is anticipated to concentrate zygotes for study. Lysogens bearing nocardiophage 0C and 0EC will be used to investigate transduction in nocardiae. Phage induced from mutant lysogens will be analyzed for their ability to transduce genetically marked nocardial strains. Lysates from lysogens will be screened for phage mutants which are less virulent than those currently available. A new mating type (MYcobacterium rhodochrous) will be studied to ascertain its role in recombinant formation with N. erythropolis Mat-cE mating type strains. Additional genetic markers will be developed in M. rhodochrous strains and the segregation and linkage of these characters determined from crosses complementary mutant of N. erythropolis.